1. Field of the Invention
The present invention relates to a layer-thickness regulator for regulating a thickness of a layer formed of a developer deposited on a surface of a developer receiver, a development unit including such a layer-thickness regulator, and an image forming apparatus including such a development unit. The invention is also concerned with a method of manufacturing the development unit.
2. Discussion of Related Art
There is known an image forming apparatus, as disclosed in JP-A-H10-333429, which forms an image by applying toner particles onto a medium such as a paper sheet and fixing the toner particles onto the medium. In this image forming apparatus, the toner particles are supplied from a toner storage onto a depository surface of a developer roller, and the toner particles are then applied by the developer roller onto a desired portion of a surface of a photosensitive drum. The toner particles are transferred from the photosensitive drum onto the medium, and the transferred toner particles are then fixed onto the medium.
Such an image forming apparatus is equipped with a layer-thickness regulator for regulating a thickness of a layer formed of the toner particles deposited on the depository surface of the developer roller, so as to make the thickness of the toner layer uniform. In the image forming apparatus disclosed in JP-A-H10-333429, the layer-thickness regulator provided in a development unit of the apparatus is constituted principally by a blade consisting of an elastic thin plate member which is made of a stainless steel or other material, so that an excess portion of the toner layer is removed by the blade so as to be dropped from of the developer roller. This blade includes a contact portion which is held in pressing contact with the developer roller, and a base portion which is held by a supporter fixed to a developer storage of the development unit. The blade is bent about 60° such that the base portion and the contact portion cooperate to define an angle of about 120°. The base portion of the blade extends upwardly from a bottom of the developer storage toward the developer roller.
In the above-described image forming apparatus, the development unit has to be necessarily given a large vertical dimension or height, since the base portion of the blade extends in the vertical or height direction of the development unit.
In general, an image forming apparatus is required to be small in size, and accordingly a development unit that is to be incorporated in the image forming apparatus is also required to be small in size Particularly, in recent years, there is a strong demand for a laser printer capable of performing a full-color printing operation. Such a color laser printer is equipped with a plurality of development units which are superposed on each other within a main body of the printer. It is therefore preferable that each of the development units has a small dimension as measured in its vertical direction, i.e., in a direction in which the development units are superposed on each other.
For reducing the vertical dimension of the development unit, it might be possible to attach a blade having the same shape as the blade disclosed in JP-A-H10-333429, to the developer storage such that the base portion of the blade extends in the horizontal direction rather than in the vertical direction. However, in this modified arrangement, for permitting the contact portion of the blade to be brought into contact with the developer roller, the base portion of the blade has to be arranged to extend from the contact portion in a direction toward the photosensitive drum, thereby making it impossible to sufficiently reduce the size of the development unit, and also causing risk of contact of the base portion of the blade with the photosensitive drum, which contact would result in deterioration in the quality of image formed in the apparatus. In this modified arrangement, even if the base portion of the blade were given a reduced length for avoiding its contact with the photosensitive drum, the vertical dimension of the development unit still can not be reduced to a sufficient extent, due to the presence of fixing means such as screw bolts required for fixing the blade to the developer storage. That is, the vertical dimension of the development unit still has to be large enough to avoid contact of the fixing means with the developer roller.
It might be also possible to attach the blade to the developer storage such that the base portion of the blade extends from the contact portion in the opposite direction, i.e., in a direction away from the photosensitive drum. However, in this modified arrangement, the contact portion of the blade is made brought into contact, at its distal end rather than at its surface, with the developer roller. Namely, the blade and the developer unit can not be held in pressing contact with each other through a sufficiently large area, whereby the thickness of the toner layer can not be reliably made uniform.